This is the Zodiac Speaking: "A Definitive Overview and Analysis of the Zodiac Case, 1966-1974," an outstanding website published and maintained by Zodiac researcher Jake Wark. This is a truly objective and highly informative site where the best essays written on the Zodiac case can be found. (Also contains a large photo section). Jake's site has been online for quite a long while, an impressive enough feat in and of itself for a privately owned and operated website. Jake has also served as a consultant for a recent book about the case. Highly recommended. 

The Zodiac Killer: Article by Jake Wark. An excellent presentation of all of the Zodiac case's basic facts, including extensive footnotes and cited sources. Featured at the Crime Library website. A must read for anyone who wants a definitive overview of the Zodiac murders.

Two New Theories Regarding the Zodiac Case: Fascinating and compelling theories by Zodiac researcher Michael F. Cole concerning aspects of the radian theory, unarguably the weirdest (and most interesting) facet of the Zodiac murder case.  Read his essay in its entirety and you will see that his guy is definitely on to something.

The Zodiac Killer and Celestial Navigation: Many researchers have long held the belief that the Zodiac killer may have had a naval background (and there is some evidence to support that idea).  Read how Michael F. Cole's latest research reveals that the Zodiac killer may have adopted his infamous name not because of the relation to astrology, as is widely assumed, but rather, because of the use of the term in celestial navigation, a science that is common in the Navy and other nautical professions.  As with any Zodiac killer hypothesis that comes from the mind of Michael Cole, this one contains very logical and highly probable assumptions.

The Bystander Blog: A sort of Zodiac murders "media watchdog" blog that offers alternative views to the all too often one-sided opinions found on Tom Voigt's commercial Zodiac killer website.  Read it and judge for yourself.

This is the Zodiac Searching: Search engine designed to return results related specifically to the Zodiac murders.  Created by Jim Nelson.  Give it a try.